Rotary filling machines are traditionally provided with a fixed support structure on which a rotating carousel is rotatably mounted. The latter carries a cylindrical tank, which contains a liquid to be bottled. In particular, the tank is filled with the liquid to be bottled up to a certain level, above which it is filled with an inert gas (such as nitrogen). This inert gas is maintained substantially at atmospheric pressure in the case of gravity filling machines, under light vacuum in the case of lightly depressed filling machines and under pressure in the case of “isobaric” filling machines.
Below the tank there are peripherally fixed a plurality of valve groups for conveying the liquid contained in the tank inside the underlying containers to be filled, such as in particular bottles, resting on corresponding support plates.
Each valve group comprises a supply duct in communication with the tank, and intercepted by a shutter which adjusts the inflow of liquid from the tank to the underlying container.
Each valve group is provided with a drainage duct of gas coming out from the container during filling.
Operationally, the container is hydraulically associated with the corresponding valve group, by raising the corresponding support plate, with the mouth of the container being brought into a sealing relationship with the supply duct of the valve group.
The supply duct shutter is then opened to allow the liquid to be dispensed into the container, and the air present in the container is conveyed into the tank or a drainage circuit (at the same pressure as the tank).
Depending on the criterion by which the filling of the container is interrupted, we can distinguish weight, volume and level filling machines.
In level filling machines, the container is filled up to a predetermined distance from its opening, a distance called “level”, established by the manufacturer of the container itself. When the container is filled at this level, the volume of product contained is equal, within certain tolerances always indicated by the manufacturer of the container, to the volume of liquid indicated on the label of the product sold.
The level may be obtained “hydraulically” or by an “electronic” control.
In “hydraulic” filling valves, the end of liquid transfer is determined by hydraulic effects, regardless of the closing of the shutter. In these valves, the air drainage duct comprises a tube which is inserted into the container during filling and through which the air exiting the container passes. This tube (referred to as “air return tube”) is provided with an open lower end, which is destined to be inserted into the container to be filled, and an open upper end which is fluidically connected to the tank or to a possible drainage circuit, to convey the air coming from the container during the filling in the latter. When the liquid dispensed into the container reaches the lower end of the return air tube, thus blocking it, the gas in the container can no longer exit and the flow of liquid is stopped. In this situation, a residual amount of the liquid rises inside the return air tube, up to reaching the same level as the level of the liquid in the tank according to the known principle of communicating vessels, thus causing the interruption of the supply of the liquid in the container.
Also in the “electronic” filling valves there is a duct for the drainage of the gas, which—unlike “hydraulic” level valves—does not necessarily include a tube intended to be introduced into the container. A probe or an ON/OFF sensor is instead introduced in the bottle. When the liquid poured into the container reaches the established level, the sensor “commands” the closing of the shutter, thus interrupting the descent of the liquid.
In isobaric filling machines, each valve group may be provided with: a first valve which can be actuated to connect, the air drainage duct (and in particular the return air tube, if present) to a suction circuit to perform a pre-drainage step of the air in the container; a second valve that can be operated to connect the return air tube to the tank during the tank pressurization and filling steps; and a third valve which can be operated to connect the return air tube to a drainage circuit (separated from the tank) to perform the decompression (degassing) of the container after the filling step.
In the following description, the term “level element” refers indistinctly to the return air tube, present in “hydraulic” level machines, or to the level probe/sensor, present in “electronic” level machines.
As is known, the filling machines described above must satisfy a series of operational requirements, which are discussed in detail below.
Accuracy of the Filling Level:
the levels obtained by positioning the return air tube or by means of a level sensor have a fairly coarse precision and repeatability. To improve the accuracy and repeatability in the execution of the correct level, a level correction function may be introduced. This function, described for example in EP0337913A2, envisages the introduction of pressurized gas into the container at the end of the filling in order to expel the liquid that has filled the bottle over the lower end of the tube through the return air tube itself. This correction technique is widespread in hydraulic level valves, although in principle it may also be extended to electronic level valves.
Automatic Format Change:
filling machines are required to process containers of different shapes, sizes and materials, and to be capable of switching from one format to another, minimising format change times and operator intervention. In particular, filling machines are required to automatically change the level height of the product poured in the bottle according to the filled container. Sometimes, this adds to the need for the level to vary, even with the same container, depending on the filling temperature of the treated product.
Protection of the Level Element:
In modern filling machines, the level element, be it a tube or a sensor, may be subject to damage due to collisions with the containers or bursting thereof. These damages cause the production to be interrupted to replace the element, thus causing the plant to lose productivity and introducing risks of contamination, as well as involving an often costly machine component. In order to prevent these damages, the valve level element is brought into the safe position until the container is correctly sealed with the supply tube of the relative valve group or the risk of burst is overcome, which may occur for example during the pressurization of the container in isobaric filling machines.
High Productivity:
In rotary filling machines, not all the valves present work simultaneously but, as will be clearer below, a portion of them is in the “dead” zone, that is, they occupy a sector in which no containers are ever present. More precisely, a starting point of the working angle is identified, at which point the containers arrive at the filling machine and enter sealed with the members of the respective valve, and an end point of the working angle, where the containers lose the seal with the valve members to exit the filling machine. The angle that joins these two points is called the “working angle” of the filling machine and encloses all the valves that are simultaneously processing the containers. The larger the working angle, the greater the productivity of the turret. One way to increase the working angle of filling turrets is to reduce the vertical travel that the containers must carry out, starting from the transfer plane thereof, to seal with the valve members. For this purpose, the more the level element is raised relative to the position corresponding to the level in the bottle, the less the displacement that the container will have to perform at the inlet and outlet of the filling machine.
Flexibility in Lifting the Return Air Tube:
to increase the productivity of the isobaric filling machines, which process carbonated drinks, one must also try to optimize the filling cycle, which as already mentioned includes the degassing step, i.e. decompression of the container. This object, as described in the Italian patent application PR92A000015, is obtained by decompressing the liquid present in the container with the level tube not in contact with the liquid, so as to also prevent the perturbation of the liquid in the container. The filling machine valves must therefore be capable of lifting the return air tube when the decompression step begins. The starting point of said step within the turret working angle is not fixed, as it depends on the working speed of the machine itself, and therefore the lifting of the level element must be “movable” in space.
The above operational requirements have all been met over the years in various ways, gradually increasing the degree of automation. If this made it possible to increase operational flexibility, it also increased the complexity and cost of filling machines. The increased automation of the machines has also implied greater risks in terms of reliability thereof.
Patent application EP0337913A2 describes a mechanical control isobaric filling machine. This machine is provided with filling valves with movable level tube and level correction system. The movement of the tube is generated by a cam follower integral with the tube itself, which engages a vertically adjustable annular cam. The cam is arranged along a circumference close to that on which the filling valves are located and is vertically moved by adjustment systems, which allow level adjustment during format change. This filling machine, managed by purely mechanical systems, allows a level correction in the bottle, a quick change in format, and a safe and reliable positioning of the level tubes. The main limitations of this machine lie in that the return air tube is not extracted from the bottle during the decompression step due to the conformation of the filling valve and in that, in any case, it is not possible to manage in a flexible manner the lifting moment of the tube when operating requirements change, as this operation is managed by angularly fixed cams.
The limits of the filling machine described in EP0337913A2 are partly overcome by the Italian patent application PR92A000015 which describes a filling machine with filling valves provided with a return air tube completely independent of the shutter, in which the decompression of the container may be carried out without having the level tube in contact with the liquid. More in detail, the turret is provided with a positioning system of the level tube comprising two devices. A first device consists of an annular abutment, in common with all the filling valves installed in the turret, which determines the level in the bottle. The second device moves the individual tube/sensor up to the level position. Operationally, the first device is used for setting the machine, normally when the format is changed before starting production. If motorized, the first device could be used to adjust to the temperature variation of the level itself. The second device consists of a pneumatic cylinder and is designed to move the single tube at each filling cycle. The mechanical activation of the cylinder of each tube by means of one or more cams suitably positioned peripherally to the turret. The position of said cams is fixed, but may be adjusted manually by the operator when setting the filling machine.
The machine described in PR92A000015, similarly to that described in EP0337913A2, does not allow a flexible management of the lifting of the tube as the operating requirements vary, as this operation is managed by means of cams. Another limitation lies in the use of the common abutment ring which, in order to be moved, requires a certain number of lifting columns connected kinematically to each other and arranged along the primitive circumference of the filling machine. “Primitive circumference” means the circumference on which the filling valves of the filling machine are arranged.
Patent EP1457457B1 has a filling valve for filling machines, also provided m this case with a level tube movable independently of the shutter. Also in this case, the tube through suitable means engages an annular cam which may be mounted on a fixed base and move vertically in a controlled manner with respect to the filling valves. The system allows the adjustment of the levels during format change (the levels may be stored in the machine control unit), as well as any movement of the level tube during the working cycle, if the cam is suitably shaped. The machine therefore allows speed in the format change, but not the optimization of the decompression step since in this case too, the tube is lifted by the cam into a fixed point independently of the rotation speed of the machine itself. Moreover, in the filling machine described in EP1457457B1, the means for transmitting the movement to the tube and the presence of an annular abutment cam make the system complex and expensive.
Italian patent application VI2005A000310 describes a filling machine with a higher degree of automation, which in particular allows a flexible management of the lifting of the tubes. More in detail, the filling machine is provided with movable tube filling valves in which the positioning of the tube is still entrusted to two devices: a ring concentric to the filling machine (mounted on board the rotating part of the machine, which acts as a reference determining the level in the bottle), and an individual movement system consisting of an electrically driven pneumatic cylinder. Compared to the solution described in PR92A000015, the electric rather than mechanical drive of the cylinders allows the tube to be moved up and down in a variable point in space. In this way, there is a greater functional flexibility of the filling valve, notwithstanding the constructive complexity and the reduced reliability of the system of PR92A000015, which are linked to the use of pneumatic cylinders, subject to wear, and to the need for a common abutment ring for all the valves, adjustable in height by means of a plurality of lifting columns to be controlled in synchronism or to be coordinated with a special kinematic chain.
The maximum level of flexibility is achieved with the filling machine described in patent application DE102005003222A1. Each filling valve is provided with a linear motor, adapted to position and move each level tube independently of the tubes of the other filling valves. In this way, maximum control flexibility is achieved, thus making the use of a common abutment ring unnecessary. The drawback of this solution is linked to the high construction cost. The use of electric motors also introduces problems related to the precision and repeatability of positioning of the level tube of the different valves and for each container processed by the same valve.
In conclusion, the degree of automation of the proposed solutions has grown over the years, but the complexity and cost of the solutions have also increased.